Pump apparatus

ABSTRACT

Provided is a pump apparatus capable of improving the performance in a wide operation range from an operation area with a low pressure and a high flow rate to an operation area with a high pressure and a low flow rate while suppressing a rated output of a motor used to drive a pump. A rotation speed of a motor  20  is controlled so that the rotation speed of the motor decreases with an increase in the load of the motor  20  driving a pump unit  10 , the rotation speed thereof increases with a decrease in the load thereof, and the load does not exceed a predetermined upper limit. For this reason, it is possible to improve the performance in a wide operation range from an operation area with a low pressure and a high flow rate to an operation area with a high pressure and a low flow rate compared to a method of the related art of uniformly keeping a rotation speed of a motor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pump apparatus that includes adriving motor, and particularly, to a pump apparatus that improves theperformance in an operation area with a high ejection pressure and a lowflow rate.

2. Description of the Related Art

In general, a vortex centrifugal pump has a small load (power necessaryfor driving a rotation shaft) in an operation area with a high pressureand a small water quantity (in a case where a distance to a drainageplace or a pump head is long or a discharge port is narrowed), but has alarge load in an operation area with a low pressure and a large waterquantity (see JP 2000-227084 A).

SUMMARY OF THE INVENTION

A motor that is used to drive a pump needs to be selected inconsideration of the maximum power necessary for the operation. In acase of a vortex centrifugal pump, the pump has the above-describedcharacteristics, and hence a motor is selected in consideration of amaximum load in a condition with a low pressure and a high flow rate.However, even when a large-power motor is selected in consideration ofthe condition with a low pressure and a high flow rate, the power isexcessively large in a condition with a high pressure and a low flowrate. That is, although the large-power motor is selected, the powerdoes not contribute to the improvement in the performance of the pump inan operation area with a high pressure and a low flow rate. For thisreason, it is useless to prepare the large-power motor for that case.

The present invention is made in view of such circumstances, and anobject thereof is to provide a pump apparatus capable of improving theperformance in a wide operation range from an operation area with a lowpressure and a high flow rate to an operation area with a high pressureand a low flow rate while suppressing a rated output of a motor used todrive a pump.

According to the present invention, since the rotation speed iscontrolled so that the rotation speed decreases with an increase in theload, the rotation speed increases with a decrease in the load, and theload does not exceed a predetermined upper limit, it is possible toimprove the performance in a wide operation range from an operation areawith a low pressure and a high flow rate to an operation area with ahigh pressure and a low flow rate while suppressing a rated output of amotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of an appearance of a pumpapparatus according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating the internal configuration of a pumpunit of the pump apparatus illustrated in FIG. 1;

FIG. 3 is a diagram illustrating an example of a control system of thepump apparatus according to the embodiment of the present invention;

FIG. 4 is a graph illustrating a relation between a throttle openingdegree and a rotation speed;

FIG. 5 is a flowchart illustrating a rotation speed control operationfrom a pump start-up timing to a pump stop timing;

FIG. 6 is a flowchart illustrating an operation involving with thecontrol of a target rotation speed;

FIG. 7 is a diagram illustrating an example in which the target rotationspeed is controlled so as to approach a relation between a predeterminedload and a rotation speed;

FIG. 8 is a flowchart illustrating an operation in a case where a loadexceeds an upper-limit value;

FIG. 9 is a flowchart illustrating an operation in a case where a loadis smaller than an upper-limit value and a target rotation speed isslower than the minimum rotation speed of FIG. 4;

FIG. 10 is a graph illustrating a relation between an ejection amount Qand a pump head H and a relation between an ejection amount Q and athrottle opening degree S; and

FIG. 11 is a flowchart illustrating a rotation speed control operationof a pump apparatus according to the other embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram illustrating an example of an appearance of a pumpapparatus according to an embodiment of the present invention. The pumpapparatus illustrated in FIG. 1 includes a pump unit 10 and a motor 20.The pump unit 10 and the motor 20 are fixed to a frame 5.

The motor 20 illustrated in FIG. 1 is an engine as aninternal-combustion engine. In order to obtain a target rotation speed,the motor (engine) 20 includes a unit (electronic governor or the like)that controls an opening degree (throttle opening degree) of a throttlevalve disposed in a suction path.

The pump unit 10 illustrated in FIG. 1 is a vortex centrifugal pump.FIG. 2 illustrates an example of the internal configuration of the pumpunit 10. The pump unit 10 includes an impeller 14 that is coupled to arotation shaft 21 of the motor 20 and a volute casing 13 thataccommodates the impeller 14. When the impeller 14 rotates, water(fluid) of a suction port 11 is carried to an ejection port 12 throughthe volute casing 13.

The pump unit 10 is, for example, a self-priming pump, and may start apumping operation even in a state where air is accumulated in asuction-side pipe in a manner such that the pump unit is started upwhile priming water is present therein. A water charging lid 15 is usedto charge priming water into the pump unit 10 at the start-up timing.

FIG. 3 is a diagram illustrating a configuration example of a controlsystem of the pump apparatus according to the embodiment of the presentinvention.

In the example of FIG. 3, the pump apparatus includes a rotation speeddetection unit 30 that detects the rotation speed of the motor 20, aload detection unit 40 that detects the load (the power necessary fordriving the rotation shaft 21) of the motor 20, and a controller 50.

For example, the rotation speed detection unit 30 converts a variationin magnetic flux of a magnet rotating along with a gear inside the motor20 into a pulse signal by a hall sensor and detects the rotation speedbased on the frequency of the pulse signal.

The load detection unit 40 is, for example, a sensor that detects theopening degree (throttle opening degree) of the throttle valve disposedin the suction path of the motor 20 as the signal involving with theload of the motor 20. This sensor includes, for example, apotentiometer.

The controller 50 is a unit that controls the operation of the motor 20and includes, for example, a micro computer. The controller 50 performsa control so that an appropriate rotation speed is obtained in responseto the load state by driving an actuator for controlling a choke valveor a throttle valve of the motor 20 in response to the signal of therotation speed detection unit 30 or the load detection unit 40.

The controller 50 includes a rotation speed controller 51 and a targetrotation speed controller 52 as the functional components involving withthe control of the rotation speed.

The rotation speed controller 51 controls the rotation speed of themotor 20 so that the rotation speed detected by the rotation speeddetection unit 30 approaches a target rotation speed Rt.

The target rotation speed controller 52 controls the target rotationspeed Rt in response to the load detection value (throttle openingdegree S) of the load detection unit 40 so that a relation between theload and the rotation speed of the motor 20 approaches a predeterminedrelation (FIG. 4).

FIG. 4 is a graph illustrating a relation between a throttle openingdegree S and a rotation speed Ra. The rotation speed Ra of FIG. 4indicates the rotation speed of the motor 20 that is determined for thethrottle opening degree S detected by the load detection unit 40. In theexample of FIG. 4, the rotation speed Ra is determined so that therotation speed decreases substantially in proportional to the throttleopening degree S. The throttle opening degree S includes, for example, anumerical range from “0” to “95”, where “0” indicates a state where thethrottle valve is fully closed and “95” indicates a state where thethrottle valve is fully opened.

The target rotation speed controller 52 may calculate the value of therotation speed Ra corresponding to the throttle opening degree S basedon, for example, a predetermined calculation formula or may read out thevalue from a data table representing in which the relation between thethrottle opening degree S and the rotation speed Ra and stored in astorage unit.

The target rotation speed controller 52 controls the target rotationspeed Rt so as to approach the relation between the throttle openingdegree S and the rotation speed Ra illustrated in FIG. 4. That is, thetarget rotation speed controller 52 controls the target rotation speedRt so that the rotation speed becomes slow when the load of the motor 20increases and the rotation speed becomes fast when the load thereofdecreases. Further, the target rotation speed controller 52 controls thetarget rotation speed Rt so that the load of the motor 20 does notexceed a predetermined upper-limit value (throttle opening degree S=80).

Further, in a case where a signal is input to the controller 50 from aswitch (not illustrated) that instructs the start-up of the pump unit10, the target rotation speed controller 52 sets the target rotationspeed Rt (for example, 4000 rpm) for the self-priming operation, whichis faster than the maximum rotation speed (3800 rpm) in the relationbetween the throttle opening degree S and the rotation speed Raillustrated in FIG. 4, to the rotation speed controller 51 (theself-priming operation mode).

After the fast target rotation speed Rt for the self-priming operationis set to the rotation speed controller 51, the target rotation speedcontroller 52 compares the throttle opening degree S detected by theload detection unit 40 with a predetermined lower-limit value. When thethrottle opening degree S exceeds the lower-limit value, the targetrotation speed controller 52 switches the current mode from theself-priming operation mode of setting the fast target rotation speed Rtfor the self-priming operation to the operation mode (the normaloperation mode) of controlling the target rotation speed Rt so as toapproach the relation between the throttle opening degree S and therotation speed Ra illustrated in FIG. 4.

Here, in a case where the throttle opening degree S is smaller than thepredetermined lower-limit value even when a predetermined time elapsesafter the target rotation speed Rt for the self-priming operation is setto the rotation speed controller 51, the target rotation speedcontroller 52 stops the rotation of the motor 20. Accordingly, it ispossible to prevent the excessive load of the motor 20 and the pump unit10 due to the fast rotation speed even when the self-priming operationmode is continued for a long period of time.

When the self-priming operation mode is switched to the normal operationmode, the target rotation speed controller 52 obtains a predeterminedrotation speed Ra corresponding to the throttle opening degree Sdetected by the load detection unit 40 in the relation between thethrottle opening degree S and the rotation speed Ra illustrated in FIG.4, and calculates a difference DR between the rotation speed Ra and thetarget rotation speed Rt set to the rotation speed controller 51. Thetarget rotation speed controller 52 compares the difference DR with apredetermined threshold value and sets a new target rotation speed Rt,which is close to the rotation speed Ra compared to the currently settarget rotation speed Rt, to the rotation speed controller 51 when thedifference DR exceeds the threshold value (the target rotation speed Rtis away from the rotation speed Ra). That is, the target rotation speedcontroller 52 sets the new target rotation speed Rt, which is includedin the range from the rotation speed Ra to the current target rotationspeed Rt and in which the difference between the rotation speed Ra andthe new target rotation speed Rt is smaller than the current targetrotation speed Rt, to the rotation speed controller 51. For example, thetarget rotation speed controller 52 sets a middle rotation speed in therange from the rotation speed Ra to the current target rotation speed Rtas the new target rotation speed Rt to the rotation speed controller 51(FIG. 7).

In a case where the throttle opening degree S of the load detection unit40 exceeds an upper-limit value (80) in the normal operation mode, thetarget rotation speed controller 52 decreases the target rotation speedRt until the throttle opening degree S of the load detection unit 40becomes smaller than the upper-limit value (80). For example, the targetrotation speed controller 52 repeats a process, which decreases thetarget rotation speed Rt by a predetermined variation amount in responseto the comparison result between the throttle opening degree S and theupper-limit value (80), until the throttle opening degree S becomessmaller than the upper-limit value (80). For example, a decrease in thetarget rotation speed Rt may be performed by subtracting a predeterminedspeed from the original speed or decreasing the entire speed by apredetermined ratio.

Next, the rotation speed control operation of the pump apparatus withthe above-described configuration will be described with reference to aflowchart.

FIG. 5 is a flowchart illustrating the rotation speed control operationfrom the pump start-up timing to the pump stop timing.

When a signal is input to the controller 50 from a switch (notillustrated) that instructs the start-up of the pump unit 10 (ST105),the target rotation speed controller 52 sets the fast target rotationspeed Rt for the self-priming operation to the rotation speed controller51 (ST125). Accordingly, the pump apparatus starts the operation at thefast rotation speed for the self-priming operation (the self-primingoperation mode).

On the other hand, the target rotation speed controller 52 switches thecurrent routine to step ST140 below in a case other than the start-up ofthe pump (for example, a case of the restart operation or the like).

When the rotation speed of the motor 20 reaches the target rotationspeed Rt for the self-priming operation by the control of the rotationspeed controller 51, the target rotation speed controller 52 obtains thethrottle opening degree S from the load detection unit 40 (ST130), andcompares the throttle opening degree S with a predetermined lower-limitvalue (ST135). Since the load of the motor 20 is noticeably low duringthe self-priming operation, the throttle opening degree S becomessmaller than the lower-limit value.

In a case where the throttle opening degree S is smaller than thelower-limit value (the self-priming operation is continued), the targetrotation speed controller 52 determines whether the time elapsing afterthe timing of setting the target rotation speed Rt for the self-primingoperation to the rotation speed controller 51 reaches a predeterminedtime (ST180). In a case where the elapse time (the time of theself-priming operation mode) is shorter than the predetermined time, thetarget rotation speed controller 52 returns the current routine to stepST130 so as to repeat the determination on whether the throttle openingdegree S exceeds the lower-limit value. In a case where the elapse timereaches the predetermined time, the target rotation speed controller 52switches the current routine to step ST155 so as to stop the rotation ofthe motor 20. Accordingly, it is possible to prevent the excessive loadof the motor 20 and the pump unit 10 when the fast rotation speed iscontinued for a long period of time in the self-priming operation mode.

When the throttle opening degree S becomes larger than the predeterminedlower-limit value (the self-priming operation ends and the waterpumping-up operation starts), the target rotation speed controller 52switches the current mode to the normal operation mode. The targetrotation speed controller 52 sets the target rotation speed Rt to apredetermined initial value (for example, 3600 rpm) (ST140), and startsto control the target rotation speed in response to the throttle openingdegree S of the load detection unit 40 (ST145). When a signal is inputto the controller 50 from a switch (not illustrated) that instructs thestop of the pump in the normal operation mode (ST150), the targetrotation speed controller 52 stops the rotation of the motor 20.

FIG. 6 is a flowchart specifically illustrating the process in stepST145 of FIG. 5, and illustrates the operation involving with thecontrol of the target rotation speed Rt in the normal operation mode.

The target rotation speed controller 52 obtains the throttle openingdegree S from the load detection unit 40 (ST205), and determines whetherthe throttle opening degree S is larger than the upper-limit value (80)(ST210). In a case where the throttle opening degree S is larger thanthe upper-limit value (80), the target rotation speed controller 52switches the current routine to step ST305 (FIG. 8) below. Further, thetarget rotation speed controller 52 determines whether the targetrotation speed Rt currently set to the rotation speed controller 51 isslower than the minimum rotation speed (3600 rpm) in the graphillustrated in FIG. 4, and switches the current routine to step ST405(FIG. 9) below in a case where the current target rotation speed Rt isslower than the minimum rotation speed.

In a case where the throttle opening degree S is smaller than theupper-limit value (80) and the target rotation speed Rt is faster thanthe minimum rotation speed (3600 rpm) in the graph illustrated in FIG.4, the target rotation speed controller 52 obtains the predeterminedrotation speed Ra (FIG. 4) corresponding to the throttle opening degreeS obtained in step ST205 (ST220), and calculates the difference DRbetween the target rotation speed Rt and the rotation speed Ra (ST225).Then, in a case where the difference DR is larger than the thresholdvalue, the target rotation speed controller 52 sets a middle valuebetween the target rotation speed Rt and the rotation speed Ra as a newtarget rotation speed Rt to the rotation speed controller 51 (ST235). Ina case where the difference DR is smaller than the threshold value, thetarget rotation speed controller 52 keeps the currently set targetrotation speed Rt.

FIG. 7 is a diagram illustrating an example of controlling the targetrotation speed Rt so as to approach the relation between the load(throttle opening degree S) and the rotation speed illustrated in thegraph of FIG. 4. The graph illustrated in FIG. 7 illustrates a part ofthe graph illustrated in FIG. 4. The points “P1” to “P3” of FIG. 7illustrate the operation points of the motor 20 expressed by thethrottle opening degree S and the target rotation speed Rt.

A rotation speed Ra1 that is set to correspond to a throttle openingdegree S1 of the operation point P1 is faster than a target rotationspeed Rt1 of the operation point P1, and the difference DR thereof islarger than the threshold value. For this reason, a middle value Rt2between the rotation speed Ra1 and the target rotation speed Rt1 is setas a new target rotation speed (ST235).

Since the new target rotation speed Rt2 is faster than the originaltarget rotation speed Rt1, the load of the motor 20 increases. For thisreason, when the target rotation speed is changed from “Rt1” to “Rt2”,the throttle opening degree becomes “S2” larger than “S1”. That is, thenew operation point P2 (S2, Rt2) moves in the right and up direction ofthe original operation point P1 (S1, Rt1). As illustrated in FIG. 7, theoperation point P2 approaches the line of the graph representing therelation between the load (throttle opening degree S) and the rotationspeed compared to the original operation point P1.

In the example of FIG. 7, the operation point moves from “P2” to “P3” bythe further control of the target rotation speed Rt. As described above,the target rotation speed Rt3 of the operation point P3 is obtained as amiddle value between the target rotation speed Rt2 and the rotationspeed Rat corresponding to the throttle opening degree S2 of theoperation point P2. The operation point P3 further approaches the lineof the graph compared to the operation point P2.

In this way, the rotation speed of the motor 20 is controlled so thatthe rotation speed approaches the relation between the load and therotation speed illustrated in the graph of FIG. 4 until the differenceDR becomes smaller than a predetermined threshold value by the repeatedprocesses of step ST205 to step ST235.

FIG. 8 is a flowchart illustrating an operation when the load (throttleopening degree S) detected by the load detection unit 40 exceeds theupper-limit value (80).

In step ST210 (FIG. 6), when it is determined that the throttle openingdegree S is larger than the upper-limit value (80), the target rotationspeed controller 52 determines whether the target rotation speed Rt setto the rotation speed controller 51 is faster than 3600 rpm (the minimumrotation speed in the graph illustrated in FIG. 4) (ST305). In a casewhere the target rotation speed Rt is slower than 3600 rpm, the targetrotation speed controller 52 sets a new target rotation speed Rt, whichis obtained by decreasing the target rotation speed Rt by apredetermined variation amount, to the rotation speed controller 51(ST325).

On the other hand, in a case where the target rotation speed Rt isfaster than 3600 rpm, the target rotation speed controller 52 sets thetarget rotation speed Rt to 3600 rpm (ST310). When the rotation speed ofthe motor 20 reaches 3600 rpm, the target rotation speed controller 52obtains the throttle opening degree S of the load detection unit 40again (ST315), and compares the throttle opening degree S with theupper-limit value (80) (ST320). In a case where the throttle openingdegree S exceeds the upper-limit value (80) even when the rotation speedis set to 3600 rpm, the target rotation speed controller 52 sets a newtarget rotation speed Rt, which is obtained by decreasing the targetrotation speed Rt by a predetermined variation amount, to the rotationspeed controller 51 (ST325).

The target rotation speed Rt of the motor 20 decreases until thethrottle opening degree S becomes smaller than the upper-limit value(80) by the repeated processes of step ST305 to step ST325 describedabove.

Furthermore, in the process illustrated in the flowchart of FIG. 8, thetarget rotation speed Rt immediately decreases to the minimum rotationspeed (3600 rpm) in a case where the load (throttle opening degree S)exceeds the upper-limit value (80) at the rotation speed faster than theminimum rotation speed (3600 rpm) in the graph illustrated in FIG. 4.Accordingly, it is possible to shorten the time in which an excessiveload is applied to the motor 20.

FIG. 9 is a flowchart illustrating an operation in a case where the load(throttle opening degree S) detected by the load detection unit 40 issmaller than the upper-limit value (80) and the target rotation speed Rtis slower than the minimum rotation speed (3600 rpm) of FIG. 4.

In this case, the target rotation speed controller 52 calculates thedifference DS between the upper-limit value (80) and the throttleopening degree S detected by the load detection unit 40 (ST405), anddetermines whether the difference DS is larger than a predeterminedthreshold value (ST410). In a case where the difference DS is largerthan the predetermined threshold value, the target rotation speedcontroller 52 sets a new target rotation speed Rt, which is obtained byincreasing the target rotation speed Rt by a predetermined variationamount, to the rotation speed controller 51 (ST415). For example, anincrease in the target rotation speed Rt may be performed by adding apredetermined speed to the original speed or increasing the entire speedby a predetermined ratio.

The target rotation speed Rt of the motor 20 increases until thedifference DS between the throttle opening degree S and the upper-limitvalue (80) becomes smaller than a predetermined threshold value by therepeated processes of step ST405 to step ST415 described above.

FIG. 10 is a graph illustrating an example of the performance of thepump apparatus. The curves CV1 and CV2 represent a relation between anejection amount Q and a pump head H, and the curve CV3 represents arelation between the ejection amount Q and the throttle opening degreeS.

The curve CV1 indicated by the dotted line represents thecharacteristics in a case where the rotation speed of the motor is keptat a rated speed (3600 rpm), and the curve CV2 indicated by the solidline represents the characteristics in a case where it is controlledsuch that the relation between the load (throttle opening degree S) andthe target rotation speed Rt approaches the relation illustrated in FIG.4.

As understood from the comparison between the curves CV1 and CV2, thepump head H increases at the same ejection amount Q by the control ofthe target rotation speed Rt. Further, the load (throttle opening degreeS) is limited so that the load does not exceed the upper-limit value(80) in an operation area in which the ejection amount Q is larger than300 [liter/min].

As described above, according to the pump apparatus of the embodiment,the rotation speed of the motor 20 is controlled so that the rotationspeed of the motor 20 decreases with an increase in the load of themotor 20 driving the pump unit 10, the rotation speed thereof increaseswith a decrease in the load thereof, and the load does not exceed apredetermined upper limit. For this reason, it is possible to improvethe performance in a wide operation range from an operation area with alow pressure and a high flow rate to an operation area with a highpressure and a low flow rate compared to the method of the related artuniformly keeping the rotation speed of the motor as indicated by thegraph of FIG. 10.

Further, according to the pump apparatus of the embodiment, since therotation speed of the motor 20 in the self-priming operation mode duringthe start-up of the pump is set to be faster than the rotation speed ofthe motor 20 in the normal operation mode, it is possible to shorten thetime until the practical pumping operation starts. Further, since thecurrent mode is automatically switched to the normal operation mode whenit is determined that the self-priming operation ends by thedetermination on whether the self-priming operation ends based on theload of the motor 20 (the throttle opening degree S), the pumpingoperation may be immediately started. Moreover, since the rotation ofthe motor 20 is stopped when the self-priming operation mode iscontinued for a predetermined time, it is possible to effectivelyprevent the excessive load of the motor 20 and the pump unit 10 frombeing continued for a long period of time due to the fast rotation speedfor the self-priming operation.

Furthermore, the present invention is not limited to the above-describedembodiment, and includes various modified examples.

FIG. 11 is a flowchart illustrating a rotation speed control operationin a pump apparatus according to the other embodiment of the presentinvention.

The flowchart illustrated in FIG. 11 is a flowchart in which step ST110to step ST120 are additionally provided between step ST105 and stepST125 in the flowchart illustrated in FIG. 5.

In this case, the target rotation speed controller 52 sets a rotationspeed (for example, 3600 rpm), which is slower than the fast rotationspeed (for example, 4000 rpm) for the self-priming operation, as theinitial target rotation speed Rt to the rotation speed controller 51before setting the target rotation speed Rt to the fast rotation speed(for example, 4000 rpm) for the self-priming operation by receiving theinput of the pump start-up signal (ST110). Then, the target rotationspeed controller 52 obtains the throttle opening degree S of the loaddetection unit 40 at the initial rotation speed (ST115), and determineswhether the throttle opening degree S is smaller than a predeterminedlower-limit value (ST120). In a case where the throttle opening degree Sis smaller than the lower-limit value, the target rotation speedcontroller 52 sets the target rotation speed Rt to the fast rotationspeed for the self-priming operation (ST125).

In this way, according to the process of the flowchart of FIG. 11, sincethe rotation speed is changed to the fast rotation speed after theself-priming operation is confirmed at the comparatively slow rotationspeed, the excessive load of the motor 20 and the pump unit 10 may beeffectively prevented.

In the above-described embodiment, in a case where the difference DRbetween the target rotation speed Rt and the rotation speed Ra (FIG. 4)corresponding to the load detection value is larger than a predeterminedthreshold value in the normal operation mode in which the load detectionvalue (throttle opening degree) is smaller than the upper-limit value(80), the middle rotation speed between the rotation speed Ra and thetarget rotation speed Rt is set to a new target rotation speed Rt(ST235, FIG. 6), but the present invention is not limited thereto. Thatis, the new target rotation speed Rt may be a rotation speed which isincluded in the range from the rotation speed Ra corresponding to theload detection value to the original target rotation speed Rt and inwhich the difference DR between the target rotation speed and therotation speed Ra is smaller than that of the original target rotationspeed Rt. For this reason, the new target rotation speed Rt is notlimited to the middle value between the rotation speed Ra and the targetrotation speed Rt as described above.

In the above-described embodiment, a case has been exemplified in whichthe pump unit 10 is the centrifugal pump, but the present invention isnot limited thereto. Specifically, various pumps may be used as the pumpunit of the present invention other than the centrifugal pump.

In the above-described embodiment, a case has been exemplified in whichthe motor 20 is the engine (reciprocating engine), but the presentinvention is not limited thereto. Specifically, variousinternal-combustion engines may be used as the motor of the presentinvention. For example, an electric motor may be used as the powersource other than the internal-combustion engine.

What is claimed is:
 1. A pump apparatus comprising: a pump; a motor thatdrives the pump; a rotation speed detector that detects a rotation speedof the motor; a rotation speed controller that controls the rotationspeed of the motor so that the rotation speed detected by the rotationspeed detector approaches a target rotation speed; a load detector thatdetects a load of the motor; and a target rotation speed regulator thatregulates the target rotation speed in response to the load detectionvalue of the load detector so as to approach a predetermined relationbetween the load and the rotation speed, the predetermined relationbeing set so that the rotation speed decreases in accordance with anincrease in the load, the rotation speed increases in accordance with adecrease in the load, and an upper-limit value of the load is set,wherein in a case where the target rotation speed regulator regulatesthe target rotation speed in response to the load detection value, thetarget rotation speed regulator calculates a difference between thetarget rotation speed set to the rotation speed controller and apredetermined rotation speed corresponding to the load detection valuein the predetermined relation, and sets a new target rotation speed,which is included in the range from the predetermined rotation speed tothe currently set target rotation speed and in which a differencebetween the new target rotation speed and the predetermined rotationspeed is smaller than the calculated difference, to the rotation speedcontroller when the calculated difference exceeds a predeterminedthreshold value.
 2. The pump apparatus according to claim 1, wherein thetarget rotation speed regulator sets a middle rotation speed in therange from the predetermined rotation speed to the currently set targetrotation speed as the new target rotation speed to the rotation speedcontroller.
 3. A pump apparatus comprising: a pump; a motor that drivesthe pump; a rotation speed detector that detects a rotation speed of themotor; a rotation speed controller that controls the rotation speed ofthe motor so that the rotation speed detected by the rotation speeddetector approaches a target rotation speed; a load detector thatdetects a load of the motor; and a target rotation speed regulator thatregulates the target rotation speed in response to the load detectionvalue of the load detector so as to approach a predetermined relationbetween the load and the rotation speed, the predetermined relationbeing set so that the rotation speed decreases in accordance with anincrease in the load, the rotation speed increases in accordance with adecrease in the load, and an upper-limit value of the load is set,wherein the target rotation speed regulator sets a minimum rotationspeed defined in the predetermined relation as the target rotation speedto the rotation speed controller when the load detection value exceedsthe upper-limit value and the target rotation speed currently set to therotation speed controller is faster than the minimum rotation speed, anddecreases the target rotation speed by a predetermined variation amountuntil the load detection value becomes smaller than the upper-limitvalue when the load detection value exceeds the upper-limit value evenafter the setting.
 4. A pump apparatus comprising: a pump; a motor thatdrives the pump; a rotation speed detector that detects a rotation speedof the motor; a rotation speed controller that controls the rotationspeed of the motor so that the rotation speed detected by the rotationspeed detector approaches a target rotation speed; a load detector thatdetects a load of the motor; and a target rotation speed regulator thatregulates the target rotation speed in response to the load detectionvalue of the load detector so as to approach a predetermined relationbetween the load and the rotation speed, the predetermined relationbeing set so that the rotation speed decreases in accordance with anincrease in the load, the rotation speed increases in accordance with adecrease in the load, and an upper-limit value of the load is set,wherein in a case where the target rotation speed regulator regulatesthe target rotation speed in response to the load detection value, thetarget rotation speed regulator increases the target rotation speeduntil a difference between the load detection value and the upper-limitvalue becomes smaller than a predetermined threshold value when thetarget rotation speed currently set to the rotation speed controller isslower than the minimum rotation speed defined in the predeterminedrelation, the load detection value is smaller than the upper-limitvalue, and the difference between the load detection value and theupper-limit value exceeds the threshold value.
 5. The pump apparatusaccording to claim 1, wherein the pump is a self-priming pump, andwherein the target rotation speed regulator sets a target rotation speedfor a self-priming operation faster than a maximum rotation speeddefined in the predetermined relation to the rotation speed controllerwhen receiving a signal for instructing the start-up of the pump.
 6. Thepump apparatus according to claim 5, wherein the target rotation speedregulator compares the load detection value with a predeterminedlower-limit value after setting the target rotation speed for theself-priming operation to the rotation speed controller, and regulatesthe target rotation speed in response to the load detection value whenthe load detection value exceeds the lower-limit value.
 7. The pumpapparatus according to claim 6, wherein the target rotation speedregulator stops the rotation of the motor when the load detection valueis smaller than the lower-limit value for a predetermined time after thetarget rotation speed for the self-priming operation is set to therotation speed controller.
 8. The pump apparatus according to claim 6,wherein the target rotation speed regulator sets an initial targetrotation speed slower than the target rotation speed for theself-priming operation to the rotation speed controller when receiving asignal for instructing the start-up of the pump, compares the loaddetection value with the lower-limit value after the setting, and setsthe target rotation speed for the self-priming operation to the rotationspeed controller when the load detection value is smaller than thelower-limit value.
 9. A pump apparatus comprising: a pump; a motor thatdrives the pump; a rotation speed detector that detects a rotation speedof the motor; a rotation speed controller that controls the rotationspeed of the motor so that the rotation speed detected by the rotationspeed detector approaches a target rotation speed; a load detector thatdetects a load of the motor; and a target rotation speed regulator thatregulates the target rotation speed in response to the load detectionvalue of the load detector so as to approach a predetermined relationbetween the load and the rotation speed, the predetermined relationbeing set so that the rotation speed decreases in accordance with anincrease in the load, the rotation speed increases in accordance with adecrease in the load, and an upper-limit value of the load is set.